Composite and Non-metallic Material Damage and Repair

These flashcards cover vocabulary related to composite material damage classification, NDI techniques, repair processes, and adhesive characteristics as detailed in the BAE Systems technical transcript.

SRM

Structural Repair Manual; used to determine whether damage is repairable and the applicable type of repair.

Damage Investigation Levels

The three initial categories used to define damage: Allowable, Repairable, and Not repairable.

Skin not-perforated damage

A category of composite surface damage that includes Abrasion, Scratches, Gouges, Nicks, Debonding, Delamination, and Dents.

Skin perforated damage

A category of composite surface damage that includes Lightning strikes, Holes, and Impact by foreign objects.

Cracks

A fracture of the laminate through the entire or partial thickness, involving both fibre breakage and matrix damage.

Warping

Dimensional distortion occurring during manufacturing (layers cooling from elevated temperatures), categorized as Cup (A), Bow (B), and Twist (C).

Longitudinal splitting

Damage in $0^{\circ}$ plies caused by Poisson's ratio mismatch between $0^{\circ}$ and $90^{\circ}$ plies, leading to matrix fracture perpendicular to the loading axis.

Delamination

A failure mode where reinforcing material layers separate from each other in the matrix, often seen at panel edge bands and around fastener holes.

BVID

Barely Visable Impact Damage; low velocity impact that leaves the outer skin looking undamaged while the underlying layers or skin-to-core bonding are significantly compromised.

Debonding

A defect where two materials (usually skin and core) stop adhering to each other.

Scratch

Damage resulting from contact with a sharp object where only surface fibres are affected.

Gouge

Damage that is wider and deeper than a scratch, affecting several plies, typically requiring a hand lay-up repair.

Abrasion

Surface damage caused by scuffing, rubbing, or scraping where fibres are not damaged and mechanical performance is not affected.

Galvanic Corrosion

Corrosion occurring when an aluminium alloy part is in direct contact with a carbon fibre surface in a corrosive environment.

Tap-testing

An NDI method using a coin or light hammer to detect debonding or entrapped water; a flat or 'dead' response indicates a potential defect.

Ultrasonic Inspection

An NDI technique using high frequency ($1$ to $30\,MHz$) acoustic waves to detect internal defects like delaminations or porosity based on wave attenuation.

Pulse echo mode

An ultrasonic NDT method where the signal is transmitted and received by the same transducer after reflecting off the back surface or a defect.

Holography (Shearography)

An optical NDI method that uses lasers to analyze interference fringes between stressed and unstressed states to reveal internal defects.

Radiograph

A photographic record produced by passing X-rays or gamma rays through a test object onto a film.

Scarfing

A technique to remove damaged composite layers one at a time, exposing surface area for the bond line by revealing $\frac{1}{2}\,inch$ of the layer below.

Autoclave

A pressure vessel operating between $120\,^{\circ}C$ and $230\,^{\circ}C$ at $7\,bars$ of pressure used to minimize voids and achieve high fibre-to-resin ratios.

Vacuum Bagging

A technique using atmospheric pressure and a nylon bag to consolidate layers, remove trapped gases, and hold heater blankets during curing.

Polyurethane adhesives

Flexible adhesives with high shear and peel strength that exhibit excellent performance at cryogenic temperatures; maximum use limits are about $300\,^{\circ}F$.

Silicones

Adhesives that remain highly elastic at $-100\,^{\circ}F$ ($-75\,^{\circ}C$) and stable up to $390\,^{\circ}F$ ($200\,^{\circ}C$), but can only handle small mechanical loads.

Anaerobic adhesives

Single component adhesives that cure in the absence of air and the presence of metal ions; typically used for metal-to-metal assemblies.